Abstract-Web applications change and are upgraded frequently due to security attacks, feature updates, or user preference changes. These fixes often involve small patches or revisions, but still, testers need to perform regression testing on their products to ensure that the changes have not introduced new faults. Applying regression testing to the entire product, however, can be very expensive, and often, companies cannot afford to do this because, typically, the turnaround time to release patches is expected to be short. One solution is focusing only on the areas of code that have been changed and performing regression testing on them. In this way, companies can provide quick patches more dependably whenever they encounter security breaches. In this paper, we propose a new regression testing approach that is applied to frequently patched web applications, considering security problems, and in particular, focusing on PHP programs. Our approach identifies the affected areas by code changes using impact analysis and generates new test cases for the impacted areas by changes using program slices considering both numeric and string input values. To facilitate our approach, we implemented a PHP Analysis and Regression Testing Engine (PARTE) and performed a controlled experiment using open source web applications. The results show that our approach is effective in reducing the cost of regression testing for frequently patched web applications.